Single-Glazed Windows VS Double-Glazed Windows

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Welcome to Sash Window Refurbish

Experts in Sash Windows Repair & Restoration, Timber Windows & Timber Doors in east midlands

Why Trust Sash Window Refurbish?

Sash Windows Refurbish specializes in providing repair and restoration services for wooden windows and doors in the UK, as well as various types of carpentry. During the process of fulfilling orders, we utilize a range of tools and paints, including saws, sprays, primers, resins, and adhesives. With more than 20 years of experience in carpentry, we have tested and used various brands and types of work tools, making us well-equipped to offer helpful advice on selecting the right tools and paints for your needs. Read more ...

What is Double Glazing?

Double glazing refers to a window having double-glazed units. The double-glazed unit consists of two panes of glass with a space between them. Technical experts refer to this space as a cavity.


This cavity usually comprises inner gases like krypton and argon. Why is this gas important? The gas works like an insulative barrier. As an insulative barrier, it helps reduce heat transmission levels and the energy bill.

This window type has a wide range of customization options. For instance, the double-glazed unit’s composition (10/8/4, 4/1/4, or 4/8/4) or it has a solar control/ low-E glass coating/ sound insulation layer.

Vacuum double glazing

Vacuum-sealed is another popular type of double glazing that’s common in historic building restoration projects. How is this type different from the standard double-glazed units? The differentiating factor is that the vacuum double glazing’s cavity has a vacuum inside.

Studies show that the vacuum transmits fewer amounts of thermal energy than inner glasses. This property makes it superior in insulation needs and helps to reduce heating bills.

The vacuum’s technical characteristics make the cavity between the two panes thinners (approximately 1 mm). Despite the narrow distance, it doesn’t affect the thermal properties. Thus, you can now get slim double glazing you can use in projects like sash window retrofitting. In contrast, you can replace single glazing in the original wooden sash windows with heritage double glazing. You can achieve this without changing the window sashes or frame.

Most individuals consider this double-glazing type a breakthrough. It’s a breakthrough as it helps keep the old historic properties more energy-efficient, and you won’t need to change the original window frame.

The latest developments in this vacuum double glazing have made these changes possible. Remember, these developments and changes weren’t available a decade ago. With these developments and properties, vacuum double glazing has become an ideal choice when having original wooden frame windows.

Low-emissivity and laminated glass

Studies show that there are a few other glass technologies individuals use for modern double-glazed units, for instance, low-emissivity glass. What is low-emissivity glass? It’s a special type of glass with a coating on its glass panes. The coating helps to reduce the heat transmission levels through the glass.

Experts also refer to it as heat-reflective or smart glass. You can also refer to the coating as Low-E glass. The uniqueness of the glass makes it vital in the constituents of double glazing. Experts use it in the composition to improve the window’s solar control properties and energy efficiency.

Lamination glass is also another popular type of safety glass. Manufacturers make the glass by bonding two glass sheets together with a layer of a given plastic in between. You can use this glass in double glazing. It helps improve the security of the windows and reduce unnecessary noise.

Single-glazing Drawbacks

Experts reveal that the main drawback of single glazing is the limited insulation they offer. These windows may let in huge amounts of cold air in the winter, making it hard to warm your house. This situation reverses in the summer, as the windows make your home extra hot and unbearable.

Thermal Efficiency

Regarding energy efficiency and insulation, single glazing has a slightly lower performance. Single glazing has a high energy transmission rate. The high transmission rate results in the easy transfer of heat from one extreme to another. During winter, it allows cold temperatures to penetrate the interior, necessitating increased heating to offset this impact.

Single glazing typically consists of a single sheet of glass. A single glass sheet is usually 4 to 6 mm thick or even thicker. It’s similar to holding a cup of boiling water, as it easily transfers heat. In contrast, double glazing acts like a thermos.

Just like how you don’t feel the heat when holding a thermos having hot water, double glazing uses layers and insulation to prevent heat from easily escaping or entering through the window.

Reduce and Insulate Against Noise

Besides having poor thermal insulation, single-glazed windows also provide limited noise reduction.

Thus, if you reside near a construction site on a busy street, the noise can be excessive and have a negative impact on your well-being.

In contrast, double-glazed windows can help minimize the amount of noise entering your home. However, the effectiveness of soundproofing varies based on the double glazing’s quality and composition.

Insufficient Security

Single glazing is more vulnerable to breakage than double glazing because it consists of a single pane of glass. This compromises your home’s security against burglars, particularly for ground-floor windows.

If you reside in an area prone to crime, your property is at an increased risk. However, using toughened double-glazing units helps to enhance the security of your house.

Condensation Is a Problem With Single-Pane Windows

Single-glazed windows are prone to generating condensation on the inside of the glass pane. The increased condensation occurs due to their high energy transmission level.

How does it happen? Condensation forms when warm indoor air meets a single glass sheet’s cold surface. This process leads to potential issues with mould and mildew inside the house. These problems can pose significant health risks if left unaddressed, particularly during winter when temperature differences are pronounced.

Retrofitting double-glazed units into your current window frames is an effective solution. How do these units help? They possess superior thermal properties that prevent condensation buildup on the inner window pane.

Reasons to Double Glaze Your Home’s Single-Glazed Windows

Despite the benefits and drawbacks of double-glazing, single-glazed windows remain prevalent in homes and commercial properties across the UK. This is especially true in regions like East Anglia and the South East. Grade 2 listed properties (with over 80,000) houses in East Anglia and more than 14,000 houses in Essex often still have single-glazed windows. However, even non-listed houses with single glazing can reap the advantages of double glazing.

What Should I Do When Living in Grade 2 Listed Home?

If you reside in a conservation area or listed building with original wooden windows, replacing them can be costly. You may also not receive approval from local conservation officers. Retrofitting double glazing becomes the practical choice in such situations.

The primary motivation for transitioning to double glazing is the rising energy costs and the desire for enhanced comfort at a lower expense. Our sash window double-glazing service caters to homeowners or individuals having single-glazed timber frame windows. Contact us for a quote or visit our pricing page for cost information.

Please note that we exclusively specialize in retrofitting double glazing for original timber frame windows. So, we do not work with UPVC or aluminium frames. As a double-glazing company, we only offer services associated with sash window double-glazing retrofitting.

U-Value of Different Types of Window Glazing 

Type U-value 
Single glazing 5 – 5.8
Triple glazing 0.6 – 1
Double glazing1.2 – 2.2 
Vacuum double glazing 0.54 – 0.7

Options for Double Glazing

If you’re seeking alternative methods for insulating your single-glazed windows and minimizing noise and heat transfer, consider secondary glazing as a viable option. Unlike retrofitting or replacing with double glazing, this alternative involves installing an additional layer of glazing on the interior of different window types, such as sash windows.

While not as energy-efficient as double glazing and less visually appealing, it can still improve your home’s comfort.

Energy Efficiency of Single-Glazed Windows

When searching for new double-glazed windows or obtaining quotes for secondary glazing, it’s crucial to assess the window’s energy rating. Why is it important to assess this rating? This rating serves as a reliable indicator of the amount of heat the window loses. Higher energy ratings signify better insulation and reduced heat loss.

Studies show that A-rated windows are the best energy-efficient alternatives. In contrast, G-rated windows offer the least energy-efficient properties, with single-glazed windows falling into the G-rated category.

However, it’s important to note that insufficient insulation is not solely attributed to single glazing. Factors such as proper window installation, window frame material, and insulated walls also significantly impact a house’s overall insulation and energy performance.

Final Thoughts

Single-glazed windows come with both pros and cons. The primary advantage is their affordability, making them cheaper than double or triple glazing. However, the main drawback lies in their inadequate energy efficiency. The inadequate energy efficiency results in heat loss, increased heating expenses, and potential condensation issues. If you reside in a listed conservation or building area, you may be obliged to retain your current window frames and opt for retrofitting double glazing onto the original wooden frames.

About the author

Glen Ramsey, who presently holds the positions of customer support and content manager, is a cherished member of the Sash Window Refurbish team. He is in a unique position to provide advice on all questions pertaining to the renovation of historic windows because he has a wealth of experience in all elements of window renovation, dealing with clients regularly and assisting them in choosing the best window-related course of action. He oversees the creation of information for all of our platforms in his capacity as content manager, including web content and other materials. Glen has witnessed the whole gamut of Sash Window Refurbish's window restoration activities, from our work on significant listed Georgian homes to a wide variety of smaller-scale private residential projects.


My technician Andrew replaced all my sash windows that had rotten sills. Accessing the rotten sills was not an easy task. He explained to me what needed to be done in order to fix the problem. He is a great person and I’m happy that he was the one who did the job. He is reliable, tidy, friendly and very professional. I highly recommend him.



I hired Andrew and Alex a while back to repair my damaged sash windows. They were was very considerate and very patient as he did his job. A few days ago, I had another problem with one of my sash lock keys and I called him again to come and fix the problem. I’m very impressed that Liam responded quickly and he not only fixed the problem but he also gave me a spare key. What a great after sales service!

Alan W.


I’m very impressed with the new windows that Andrew installed and also the reconditioning job that he did on other sash windows. The quality of his work is by far more superior than what we got when we hired another company a few years back. We will certainly hire him again if any window work arises

Kelly (Sleaford)


Our decorator referred us to Andrew because some of the work needed a window expert. Andrew together with our decorator did a fantastic job. The work was done efficiently and to the highest standards. Andrew is understanding, committed and very professional. I recommend him without any hesitation.

Steaven Reader


Alex did a great job in fixing windows in our terraced house. The windows were broken, frames damaged and the wood was also rotten. Alex's job was high quality and he did it pretty fast. I was also very impressed that he was considerate of my son’s asthma condition and maintained cleanliness. Top work.



Andrew just recently replaced three sash windows in my Edwardian house. He also repaired and replaced some sills and draught proofed three windows. In addition to that, he also did some carpentry work. What I like the most about Liam is that he did a clean job. He is very professional and always updated me about the timescales and costs. He also did his job with minimal disruptions. I highly recommend him.

Cris M.